The present invention relates to ophthalmic lenses having inserts for projecting an image towards the user, and more specifically, for attenuating parasitic images in such a lens.
U.S. Pat. Nos. 5,886,822 and 6,204,974 disclose image combination systems for eyeglasses or face masks; an image is projected towards the wearer's eye via an optical path made in the lens; in these patents, as in the present description, the optical system containing the inserts is called a “lens”, which system may especially be intended to be mounted in an eyeglass frame or in a head-mounted display. In one embodiment, this optical path is defined by inserts mounted in the thickness of the lens; the inserts proposed in these patents comprise mirrors, semireflective plates, polarizing beam-splitter cubes, quarter-wave plates, lenses, mirrors, concave reflecting lenses (for example, a Mangin mirror), diffractive lenses and/or holographic components. It is proposed to mount these inserts in the lens in an injection moulding, or else to machine the insert and to assemble them with the other elements of the lens.
In the example of FIG. 4 of U.S. Pat. No. 5,886,822, the lens is formed by mounting a cube-shaped insert between two glass or plastic plates. A first polarizer is placed around the insert between the two glass plates; the insert is designed so as to transmit the polarization in the same direction as the first polarizer; a second polarizer is mounted so that it can rotate on a support in front of the glass plate away from the user's eye. This lens allows the user to see both the light projected through the insert and the light coming from the ambient scene, which passes around the insert and through the latter. This ambient light passes through both polarizers or the second polarizer and the insert. Rotation of the second polarizer allows the user to adjust the balance between the projected image and the ambient image. In the example of FIG. 8, it is proposed to use a liquid-crystal panel and a sensor in order to compensate or balance the relative brightnesses of the projected image and of the ambient image automatically. In this document (col. 11 line 51) it is also proposed to use photochromic materials in order to control the ambient light. No details are given concerning the use of such materials. Finally, this document also suggests masking the presence of inserts by polarizing, photochromic, tinted or reflecting films, as for sunglasses; these films are only used for aesthetic purposes.
The invention is based on the discovery of a problem relating to parasitic images in lenses having inserts. FIG. 1 shows, by way of example, a lens in which this problem appears. It shows an outline diagram of a lens of the type proposed in FIG. 7 of U.S. Pat. No. 5,886,822. The ophthalmic lens 2 is an optical system formed from a material 4, in which an insert 6 is placed; the insert 6 sends the light coming from a source 12 through a focusing lens 8 towards the user's eye 10; the light coming from the source 12 is injected into the thickness of the ophthalmic lens through a focusing lens 14 placed at the periphery of the ophthalmic lens. The light coming from the external environment passes through the insert 6 and the focusing lens 8 and also arrives at the user's eye. The latter can therefore see both the image coming from the source 12 and the external environment.
The image coming from the source is projected from the focusing lens towards the insert, and is transmitted through the insert towards the user's eye. However, it is possible for the light coming from the source to be reflected on the front wall 15 of the lens, thus forming a parasitic image, hereinafter called front image or front parasitic image. It is also possible for the light coming from the source to be reflected on the rear wall 16 of the lens thus forming another parasitic image, hereinafter called rear image or rear parasitic image. The dotted lines in FIG. 1 symbolize the propagation of the direct image, and of the images reflected on the front and rear walls of the lens.
FIG. 2 shows schematically the projected images, as seen by the user. The image 18 is the image projected directly from the focusing lens towards the insert; the images 20 and 22 are the parasitic images projected after respective reflections on the front and rear faces of the lens. These parasitic images may have a brightness close to that of the main image. Effectively, given the reflection angles proposed in the example, the reflection is a total internal reflection.
U.S. Pat. 6,124,977, discloses an image display apparatus using a modified prism as the optical system. Images to be displayed are applied to a first prism surface by a display device. They are reflected at a third surface of the prism and then on the second surface after passing through the third surface, to arrive at the user's eye. The second prism surface is provided with a reflective coating and in places, with a black absorbent coating. This apparatus does not comprise an insert that receives light propagating in a lens and redirects this light to the user's eye.